Objectives: The over-recruitment and activation of leukocytes characteristic of early atherosclerosis is considered the driving force behind atheroma development and is regulated by the concerted activities of several cytokines, chemokines and adhesion molecules surrounding a lipid core. Low serum testosterone levels are associated with cardiovascular disease in men and clinical trials demonstrate that testosterone replacement therapy (TRT) improves symptoms and reduces the inflammatory burden of atherosclerosis. This study investigates whether the known atheroprotective effect of testosterone in the testicular feminised (Tfm) mouse model1 is associated with an effect on inflammatory factors.
Methods: Tfm mice express a non-functional androgen receptor (AR) and low levels of circulating testosterone. Tfm mice were fed a high-cholesterol diet (42% butterfat, 1.25% cholesterol and 0.5% cholate) ad libitum for 28 weeks and received either physiological testosterone replacement (intramuscular mixed testosterone esters, Sustanon 100®, 25 mg/kg) or placebo (saline) and were compared to wild type littermate controls. Aortic root serial sections were analysed by oil red O staining and percentage lipid deposition calculated. Presence of inflammatory cells was investigated by immunohistochemistry in addition to expression of the novel inflammatory chemokine, CX3CL1. Blood was analysed for testosterone, 17β-estradiol, lipids and cytokines (TNFα, IL6, IL1β, IL10 and MCP-1). Investigators were blinded to treatment group throughout sample analysis (ANOVA).
Results: TRT reduced lipid deposition in Tfm mice receiving a high cholesterol diet compared to placebo (2.15±0.17 vs 4.70±1.04%, respectively; P=0.05), but demonstrated no effect on serum lipids and cytokines. Immunohistochemistry detected monocyte infiltration locally adjacent to lipid streaks. CX3CL1 and its receptor were detected in plaque regions but were not influenced by testosterone or AR function (n=6).
Discussion: Physiological concentrations of testosterone can inhibit fatty streak formation, via AR-independent mechanisms in Tfm mice, although not through systemic anti-inflammatory actions or local effects on chemokine expression.